The present invention relates to an optical position measurement system employing one or more linear detector arrays. Typical optical measurement systems used for motion capture applications use multiple cameras to maintain a line of site to emitters placed on a movable object. Each camera must be calibrated with respect to all other cameras to arrive at a common coordinate system. Furthermore, the cameras that are used typically employ CCD arrays, each containing large numbers of elements so that processing of signals is intensive and costly. A system that could maintain accuracy while reducing costs and complications in measuring would provide significant advantages over the prior art. It is with these thoughts in mind that the present invention was developed.
The present invention relates to an optical position measurement system employing one or more linear detector arrays. The present invention includes the following interrelated objects, aspects and features:
(1) In a first embodiment of the present invention, a single linear array of bi-cell optical detectors is arranged with each bi-cell detector having a rectangular aperture located a prescribed distance above the surface of the bi-cell detector. While two or three such detectors in a linear array would be sufficient for most measurements, in order to accommodate to the fact that one or more detectors in an array may be blocked from line of sight with the point source emitter at any one time or another, in the preferred embodiment, at least four and perhaps eight or more detectors in a linear array may be provided. Each bi-cell detector has an active area including at least two detecting regions adjacent one another. Bi-cell optical detectors allow detection that is not dependent on uniformity of source radiation, but is only dependent on the angle of incidence of source radiation.
(2) As in any position measurement system, it is important to ensure that resolution of emitter position over a wide range of emitter locations is kept as high as possible. Typically, high resolution of far away emitter positions requires large spacing between adjacent detectors. Conversely, to achieve high resolution at close ranges, the detectors are preferably wide angle detectors closely spaced apart. In order to accommodate to all different lengths of ranges between the point source emitter and the detector array, in the preferred embodiment, a large number of detector locations are used while keeping each detector as simple as possible.
(3) In the first embodiment of the present invention, in calculating the position of a point source emitter, it is understood that each detector receives light from the point source emitter at a unique angle different from the angles at which the other detectors receive light from the point source emitter. A plot of detector ratios is made by taking the best fit line through the ratios from each detector and the location of the point where the detector ratio is zero yields the point of perpendicularity between the emitter and the linear detector array. This location is determined by calculating, for each detector, the tangent of the angle of incidence of a beam of light at each detector.
(4) The same principles set forth above concerning a one dimensional detector array are equally applicable to determine the particular location of a point source emitter in two or three dimensions. In the example of a three dimensional detector, three linear arrays of bi-cell detectors are arranged at the periphery of a measuring space mutually orthogonal to one another. Calculations of the x, y and z intercepts through calculations of the tangent of the angle between each detector and the point source emitter allows one to calculate the x, y and z coordinates of the point source emitter.
As such, it is a first object of the present invention to provide an optical position measurement system employing one or more linear detector arrays.
It is a further object of the present invention to provide such a device in which, in one embodiment thereof, a multiplicity of bi-cell detectors are arranged spaced from one another along a single line.
It is a still further object of the present invention to provide such a system in which each bi-cell detector has a rectangular aperture located thereabove at a prescribed spacing therefrom.
It is a still further object of the present invention to provide such a device designed to measure in two or three dimensions.
It is a still further object of the present invention to provide such a device which includes one linear array of detectors for each dimension of measurement contemplated with the arrays being mutually orthogonal.
These and other objects, aspects and features of the present invention will be better understood from the following detailed description of the preferred embodiments when read in conjunction with the appended drawing figures.